Advent of Code 2024 - Day 2

Section

inputs = File.read!(File.cwd!() <> "/advent-of-code/2024/day02.input")
|> String.split("\r\n")
|> Enum.map(fn line -> String.split(line) |> Enum.map(&amp;String.to_integer/1) end)

direction_ok? = fn ns ->
  (ns == Enum.sort(ns, :asc)) or (ns == Enum.sort(ns, :desc))
end

deltas_ok? = fn ns ->
  Enum.zip(ns, Enum.drop(ns, 1))
  |> Enum.all?(fn {a, b} -> 1 <= abs(a-b) and abs(a-b) <= 3 end)
end

defmodule Day2 do
  def test(xs) do
    direction_ok?(xs) and deltas_ok?(xs)
  end

  def direction_ok?(ns) do
    (ns == Enum.sort(ns, :asc)) or (ns == Enum.sort(ns, :desc))
  end
  
  def deltas_ok?(ns) do
    Enum.zip(ns, Enum.drop(ns, 1))
    |> Enum.all?(fn {a, b} -> 1 <= abs(a-b) and abs(a-b) <= 3 end)
  end
end

inputs
|> Enum.filter(&Day2.test/1)
|> Enum.count()

inputs
|> Stream.map(fn xs -> Enum.map(0..(length(xs)-1), &List.delete_at(xs, &1)) end)
|> Stream.map(fn xs -> Enum.filter(xs, fn ys -> Day2.test(ys) end) end)
|> Enum.count(&Enum.any?/1)

#650 too high
#633 too low

# Failed at:  [1,2,3,2,4]
# Why?  Because we were calling List.delete so deleting the second 2 was actually deleting 
#    first 2